I'm making a huge level. To get a better texture quality i'm using around 100 hmp-terrains, which are dynamically loaded, if my player gets near them. (using ent_create). If player moves away - terrains are removed by ent_remove. Everything works fine, but when the entity is removed - the RAM memory (reserved for texture i supose) doesn't free - so it grows and grows!!! Can i manually clear it?
Oh, and one more thing: ent_create'ing a hmp-terrain in real-time kills my fps for a moment. Can this proccess work parallel without making the game process stop waiting for terrain to be loaded?

try ent_purge after ent_remove

For deleting models/terrains in the cache you must load the level again, or use level_mark/level_free.

I wonder, how can i load a level in real-time in a racing game?

I don't know, but maybe a good bet would be to use the two terrains, and deform them according to a 2d array of vertex values, and if required change the skin. That way, you can alternate between the terrains that the player is on. However, you would have to set up and array management system for the vertexes, and for alternating between terrains.

Too difficult and the result would be less than expected. So I guess the only way to do this is to find the ballance between my memory and my ideas. But I think it'll be really hard to fit 2sqr kilometers of reasonable quality of terrain in 100mb of RAM.